256 Precision Measurements of Photoresist film Thicknesses Using Scanning White Light Interferometry

Accurate measurement of photoresist film thickness and its uniformity is very important to the performance of all photoresist devices. Effective inspection of the film thickness and uniformity is the key to high performance of the devices. Conventionally, the film thicknesses are measured using a spectrophotometer/reflectometer, an ellipsometer or a physical step measurement. Scanning white light interferometry (SWLI) is an established technique to measure the surface topography. This technique offers many advantages in measurement such as speed, ease of use and accuracy. A useful extension of SWLI is the ability to measure films larger than about 1.5 ?m. The recently introduced ‘helical complex field’ (HCF) function now allows film thicknesses to be measured down to ∼25 nm (index dependent). This new method combines novel Coherence Correlation Interferometry (CCI) with sub-nanometre vertical resolution and ∼1 μm lateral resolution and can therefore be used for precision measurement of thin films. In this paper, the fundamentals of the techniques are described and some results from SiO2 and photoresist on Si substrate are presented.